headers: Support default header values in Caddyfile with '?' (#3807)

* implement default values for header directive

closes #3804

* remove `set_default` header op and rely on "require" handler instead

This has the following advantages over the previous attempt:

- It does not introduce a new operation for headers, but rather nicely
  extends over an existing feature in the header handler.
- It removes the need to specify the header as "deferred" because it is
  already implicitely deferred by the use of the require handler. This
  should be less confusing to the user.

* add integration test for header directive in caddyfile

* bubble up errors when parsing caddyfile header directive

* don't export unnecessarily and don't canonicalize headers unnecessarily

* fix response headers not passed in blocks

* caddyfile: fix clash when using default header in block

Each header is now set in a separate handler so that it doesn't clash
with other headers set/added/deleted in the same block.

* caddyhttp: New idle_timeout default of 5m

* reverseproxy: fix random hangs on http/2 requests with server push (#3875)

see https://github.com/golang/go/issues/42534

* Refactor and cleanup with improvements

* More specific link

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>
Co-authored-by: Денис Телюх <telyukh.denis@gmail.com>

1 files changed, 19 insertions, 6 deletions

diff --git a/modules/caddyhttp/reverseproxy/caddyfile.go b/modules/caddyhttp/reverseproxy/caddyfile.go
index c5f8e17..003f676 100644
--- a/modules/caddyhttp/reverseproxy/caddyfile.go
+++ b/modules/caddyhttp/reverseproxy/caddyfile.go
@@ -480,6 +480,8 @@ func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 				h.BufferRequests = true
 
 			case "header_up":
+				var err error
+
 				if h.Headers == nil {
 					h.Headers = new(headers.Handler)
 				}
@@ -487,18 +489,25 @@ func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 					h.Headers.Request = new(headers.HeaderOps)
 				}
 				args := d.RemainingArgs()
+
 				switch len(args) {
 				case 1:
-					headers.CaddyfileHeaderOp(h.Headers.Request, args[0], "", "")
+					err = headers.CaddyfileHeaderOp(h.Headers.Request, args[0], "", "")
 				case 2:
-					headers.CaddyfileHeaderOp(h.Headers.Request, args[0], args[1], "")
+					err = headers.CaddyfileHeaderOp(h.Headers.Request, args[0], args[1], "")
 				case 3:
-					headers.CaddyfileHeaderOp(h.Headers.Request, args[0], args[1], args[2])
+					err = headers.CaddyfileHeaderOp(h.Headers.Request, args[0], args[1], args[2])
 				default:
 					return d.ArgErr()
 				}
 
+				if err != nil {
+					return d.Err(err.Error())
+				}
+
 			case "header_down":
+				var err error
+
 				if h.Headers == nil {
 					h.Headers = new(headers.Handler)
 				}
@@ -510,15 +519,19 @@ func (h *Handler) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
 				args := d.RemainingArgs()
 				switch len(args) {
 				case 1:
-					headers.CaddyfileHeaderOp(h.Headers.Response.HeaderOps, args[0], "", "")
+					err = headers.CaddyfileHeaderOp(h.Headers.Response.HeaderOps, args[0], "", "")
 				case 2:
-					headers.CaddyfileHeaderOp(h.Headers.Response.HeaderOps, args[0], args[1], "")
+					err = headers.CaddyfileHeaderOp(h.Headers.Response.HeaderOps, args[0], args[1], "")
 				case 3:
-					headers.CaddyfileHeaderOp(h.Headers.Response.HeaderOps, args[0], args[1], args[2])
+					err = headers.CaddyfileHeaderOp(h.Headers.Response.HeaderOps, args[0], args[1], args[2])
 				default:
 					return d.ArgErr()
 				}
 
+				if err != nil {
+					return d.Err(err.Error())
+				}
+
 			case "transport":
 				if !d.NextArg() {
 					return d.ArgErr()